1. Field of the Invention
The present invention relates to a vehicle suspension system for a steerable wheel and more particularly, to a vehicle suspension system for a steerable wheel which can improve running safety, handling safety and ride comfort by easily defining an imaginary kingpin and increasing a free lay out degree with respect to a change in camber and caster angles.
2. Description of the Related Art
In general, a vehicle suspension system for a steerable system connects an axle shaft and a vehicle body to each other and controls a position of a wheel with respect to the vehicle body to obtain a better positioning in a vehicle motion. The axle shaft is thereby prevented from directly transmitting impacts or vibrations from a road surface to the vehicle body, so that there can be obtained an optimal handling safety, a reduction in damage to baggage, and an improved ride comfort.
Particularly in steerable front suspension, the suspension should be designed to absorb vibrations or impacts from the road surface as well as obtain running safety by maintaining an optimal position during a vehicle's straight travelling and maintaining a handling safety during a vehicle's turning.
The front wheel is mounted to be turned in its direction from right to left or from left to right, centering the king axis, and is also mounted with a geometrical angle to meet the requisite for the front suspension.
Mounting the front wheel with the geometrical angle is called wheel alignment. The wheel alignment is determined by several elements, but the optimal operation of the front wheel is, however, achieved by the supplemental operation of the elements with respect to each other. A kingpin inclination among the elements reduces a handling force of a steering wheel with a camber, absorbs any impact generated from the vehicle motion and then increases a restitution force of the steering wheel. The running safety of the straight ahead position of the vehicle and the handling safety in a vehicle's turning position are thereby obtained.
The kingpin inclination is such that the kingpin is mounted with its center line lying at a predetermined angle with respect to the vertical line when the vehicle is viewed from the front. The interval between the center line of the kingpin and the center line of the wheel is called spindle offset. The offset at the wheel center has an effect on the motion of vehicle when a driving force and an engine brake are applied to the wheel. The offset at the ground has an effect on the handling safety when vehicle brakes and turns. If the offset at the ground is decreased, the sensitivity with respect to the steering is decreased, in the same manner as the handling safety is increased when the vehicle brakes and turns.
When the steerable wheel moves up and down, the change in the camber angle and the tread should be small, so that better straight ahead safety can be obtained.
Referring to FIG. 7A, there is shown a general double Wishbone type suspension system. In this suspension system, a pair of upper arms 53 are connected to the upper parts of the knuckle 52 supporting the wheel. The car body side ends of the pair of upper arms 53 which are spaced from each other along the longitudinal direction with respect to vehicle body are connected to the car body. A pair of lower arms 54 connect to the lower part of the knuckle 52 with the vehicle body. A lower end of a strut assembly shock absorber system 55, is connected to the intermediate location of the lower arm 54.
Accordingly, the up-down vibrations applied to the front wheel are absorbed by the strut assembly. The upper and lower arms 53 and 54 are pivoted upward and downward on the hinge point of their car body side ends.
However, the location of ball joints where the outer ends of the upper and lower arms are connected to the knuckle is fixed. The kingpin axis K is formed by a line connecting the ball joint of the upper arm to that of the lower arm. This kingpin axis is always fixed, so that, in accordance with mechanical characteristics, installation of the kingpin axis, the camber angle, the tread, and the height of roll center are substantially restricted.
At the time of the up-down vibrations which are generated when the vehicle is turning or running on an uneven road, the changes in the camber angle and the tread show the opposite characteristics to each other. Accordingly, since the more the camber angle is changed, the more the tread is changed, and the ride comfort deteriorates. If the change in the tread is small, that of the camber angle is also small, resulting in a deterioration of handling safety.
Namely, the changes in the camber angle and the tread have a great effect on the ride safety and the handling safety. In a conventional suspension system, a connection of the upper arm to the knuckle is performed by a fixing point such as one ball joint, so that, the camber and the tread can be alternatively installed due to its structure.